U.S. patent number 7,281,328 [Application Number 11/253,973] was granted by the patent office on 2007-10-16 for method of fabricating rigid-flexible printed circuit board.
This patent grant is currently assigned to Samsung Electro-Mechanics Co., Ltd.. Invention is credited to Dong Gi An, Jung Hun Chai, Jung Wook Hwang, Kwang Yune Kim, Yang Je Lee, Young Ho Lee, Dek Gin Yang, Kyu Hyok Yim.
United States Patent |
7,281,328 |
Lee , et al. |
October 16, 2007 |
Method of fabricating rigid-flexible printed circuit board
Abstract
The present invention is related to a method of fabricating a
rigid-flexible printed circuit board. Specifically, this invention
relates to a method of fabricating a rigid-flexible printed circuit
board, in which an internal circuit pattern exposed for use in an
external pad and a mounting pad is protected from external
environments using a resist cover by window etching the base copper
foil of a flexible region upon formation of an external circuit
pattern as opposed to using a resist cover. Thus the number of
fabrication processes and the fabrication costs are decreased and
the increase in defect rates due to contamination is prevented,
resulting in maximized reliability.
Inventors: |
Lee; Yang Je
(Chungcheongbuk-do, KR), Yang; Dek Gin
(Chungcheongbuk-do, KR), Hwang; Jung Wook
(Gyeongsangnam-do, KR), Yim; Kyu Hyok
(Chungcheongbuk-do, KR), Chai; Jung Hun
(Jeollabuk-do, KR), Lee; Young Ho (Daegu,
KR), Kim; Kwang Yune (Daejeon, KR), An;
Dong Gi (Chungcheongnam-do, KR) |
Assignee: |
Samsung Electro-Mechanics Co.,
Ltd. (Kyunggi-Do, KR)
|
Family
ID: |
36384592 |
Appl.
No.: |
11/253,973 |
Filed: |
October 18, 2005 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20060101640 A1 |
May 18, 2006 |
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Foreign Application Priority Data
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Oct 28, 2004 [KR] |
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10-2004-0086731 |
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Current U.S.
Class: |
29/852; 29/847;
29/846; 174/262; 427/97.1; 427/97.7; 174/254 |
Current CPC
Class: |
H05K
3/4691 (20130101); Y10T 29/49165 (20150115); H05K
3/4652 (20130101); Y10T 29/49147 (20150115); Y10T
29/49155 (20150115); Y10T 29/49156 (20150115); H05K
2201/09127 (20130101); H05K 3/28 (20130101) |
Current International
Class: |
H01K
3/10 (20060101) |
Field of
Search: |
;29/846,847,852
;174/262,254,255 ;427/97.1,97.7 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Chang; Richard
Attorney, Agent or Firm: Darby & Darby P.C.
Claims
What is claimed is:
1. A method of fabricating a rigid-flexible printed circuit board,
comprising the steps of: providing a base substrate having a
polyimide layer and an internal circuit pattern formed on at least
one of an upper or a lower surface thereof; forming a coverlay, to
protect the internal circuit pattern, on a corresponding flexible
region of the base substrate that excludes a pad portion of the
corresponding flexible region; placing prepregs on the upper and
lower surfaces of the base substrate on a corresponding rigid
region, placing base copper plates on the prepregs on the
corresponding rigid region and the corresponding flexible region on
the prepregs, and collectively laminating the placed prepregs and
base copper plates to form a rigid region and a flexible region;
forming external circuit patterns electrically connected to each
other on the rigid region, while the base copper plate serves to
protect the flexible region; and removing the base copper plate
corresponding to the flexible region after the forming step has
formed the external circuit patterns.
2. The method as set forth in claim 1, wherein the pad portion of
the flexible region is a region for use in an external pad and a
mounting pad.
3. The method as set forth in claim 1, wherein the base copper
plate on the corresponding flexible region is formed to be about
0.05 to 5 mm larger than the flexible region.
4. The method as set forth in claim 1, wherein the removing step
further comprises the steps of: processing a portion of the base
copper plate corresponding to a boundary between the flexible
region and the rigid region using a computer numerical control
(CNC) drill or a steel rule die; and physically removing the base
copper plate.
5. The method as set forth in claim 1, wherein the step of forming
the external circuit patterns further comprises the steps of:
forming a through hole through the rigid region; plating the base
copper plate, on the corresponding rigid region having the through
hole formed therethrough and the corresponding flexible region,
with copper to form a plated layer; and partially removing the base
copper plate and the plated layer on the corresponding rigid region
to form the external circuit pattern, while the base copper plate
serves to protect the flexible region.
Description
INCORPORATION BY REFERENCE
The present application claims priority under 35 U.S.C. .sctn.119
to Korean Patent Application No. 10-2004-0086731 filed on Oct. 28,
2004. The content of the application is incorporated herein by
reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates, generally, to a method of
fabricating a rigid-flexible printed circuit board (rigid-flexible
PCB), and more particularly, to a method of fabricating a flying
tail type rigid-flexible PCB that eliminates the need for a resist
cover serving to protect a pad portion exposed for use in an
external pad and a mounting pad from external environments, by
window etching the base copper foil of a flexible region upon the
formation of an external circuit pattern, instead of using the
resist cover.
2. Description of the Related Art
Recently, while the degree of integration of semiconductor devices
is gradually increasing, the number of pads provided on
semiconductor devices to connect the semiconductor devices to
external circuits is increasing and the mounting density is also
increasing. For example, when a minimum processing dimension on the
semiconductor device formed of silicon is about 0.2 .mu.m, about
1000 pads may be provided on a semiconductor device having a size
of about 10.times.10 mm.
Further, in semiconductor apparatuses, such as semiconductor
packages, having the semiconductor devices mounted thereon, the
size and thickness of the apparatus should be decreased to increase
the mounting density. In particular, small and thin semiconductor
packages are required for portable information apparatuses, such as
notebook type PCs, PDAs, mobile phones, etc.
For packaging the semiconductor device, while the semiconductor
device is mounted on a wiring substrate, the pad of the
semiconductor device should be connected to the pad of the wiring
substrate. However, in the case where about 1000 pads are provided
on the about 10.times.10 mm sized semiconductor device, they come
to have fine pitches of about 40 .mu.m. Hence, with the aim of
connecting the pad having the fine pitch of the semiconductor
device to the pad of the wiring substrate, very high accuracy is
required for wiring on the wiring substrate or position-matching
upon connection. Eventually, it is difficult to apply conventional
wire bonding techniques or tape automated bonding (TAB)
techniques.
To solve the problem, the use of a rigid-flexible PCB having rigid
and flexible regions interconnected without the use of an
additional connector by structurally bonding a rigid substrate and
a flexible substrate together is more and more frequently proposed.
In particular, the rigid-flexible PCB is mainly applied to small
terminals, such as mobile phones, realizing high integration by
removing unnecessary space due to the use of the connector,
depending on requirements of fine pitches and high integration of
mounting parts in proportion to high functionality of the mobile
apparatuses.
Although the rigid-flexible substrate is manufactured in the most
commonly used rigid-flexible-rigid form or the rigid-flexible form,
the present invention is directed to a flying tail type comprising
only rigid-flexible regions.
Referring to FIGS. 1A to 1I, a conventional process of fabricating
a flying tail type rigid-flexible PCB is sequentially shown.
In a polyimide copper clad laminate 10 including a polyimide layer
11 and a copper foil 12, the copper foil 12 is subjected to a
photolithographic process to form an internal circuit pattern
having a predetermined shape (FIG. 1A).
Then, to protect the internal circuit pattern corresponding to a
flexible region, which is to be formed on the polyimide copper clad
laminate 10, from the external environment, a polyimide film 20 is
processed to suit the flexible region.
The processed polyimide film 20 is attached to the part of the
flexible region having the corresponding internal circuit pattern,
using an adhesive, after which the polyimide film 20 is temporarily
bonded through manual soldering, thereby completing the process of
forming a coverlay (FIG. 1B).
After the formation of the coverlay corresponding to the part of
the flexible region using the polyimide film 20, a resist cover 30
is formed on the other part of the flexible region (FIG. 1C).
The resist cover 30 functions to protect the internal circuit
pattern exposed for use in an external pad and a mounting pad from
external environments, and includes, for example, heat-resistant
tape or peelable ink. In addition, the resist cover 30 is removed
after the completion of the substrate, unlike the polyimide film
20.
Subsequently, to confer mechanical strength and adhesive strength
to a rigid region, which is to be formed on the polyimide copper
clad laminate 10, prepregs 40 and base copper plates 50 are
laminated on the upper and lower surfaces of the base substrate to
face each other.
After the prepregs 40 and the base copper plates 50 are laminated,
they are compressed using a press, to form both a rigid region, in
which the circuit pattern is incorporated into the prepreg, and a
flexible region, in which the circuit pattern is covered with the
coverlay (FIG. 1D).
Then, a through hole 60 for electrical connection between internal
and external layers is formed (FIG. 1E). The base copper plate 50
and the through hole 60 are plated with copper to form a copper
plated layer 70 (FIG. 1F). During the plating, an external circuit
pattern having a predetermined shape is formed (FIG. 1G).
The external circuit pattern is obtained using a predetermined
photolithographic process, and the plated layer of the flexible
region is etched therewith.
After the external circuit pattern having a predetermined shape is
formed, the resist cover 30 is removed.
In the case where the resist cover is formed of peelable ink,
peelable ink may be easily removed by further applying peelable ink
on the formed peelable ink to form an ink layer having a
predetermined thickness and then removing the ink layer (FIG.
1H).
Thereafter, the resultant substrate is coated with PSR ink (photo
imageable solder resist mask ink) and then surface treated, thereby
finally completing a flying tail type rigid-flexible PCB, in which
the flexible region is covered with the coverlay, including the
polyimide film and the resist cover (FIG. 1I).
However, in the flying tail type rigid-flexible PCB thus formed,
since the external pad or mounting pad of the flexible region is
internally exposed, processes of forming the resist cover on the
flexible region using the heat-resistant tape or peelable ink and
then removing it are required, causing problems of undesirably
complicating fabrication processes and of increasing fabrication
costs.
Further, due to the residue remaining after the removal of the
heat-resistant tape or peelable ink, contamination may occur, thus
a defect rate is increased, resulting in drastically decreased
reliability.
SUMMARY OF THE INVENTION
Accordingly, the present invention has been made keeping in mind
the above problems occurring in the related art, and an object of
the present invention is to provide a method of fabricating a
flying tail type rigid-flexible PCB, which is advantageous because
a resist cover is not used and a base copper foil of a flexible
region is window etched after the formation of an external circuit
pattern, thereby decreasing the number of fabrication processes and
the fabrication costs and preventing contamination, thus reducing a
defect rate, resulting in maximized reliability.
In order to achieve the above object, the present invention
provides a method of fabricating a flying tail type rigid-flexible
PCB without the need for a resist cover, which includes the steps
of providing a base substrate including a polyimide film having an
internal circuit pattern formed on at least one surface thereof;
forming a coverlay to protect the internal circuit pattern
corresponding to a flexible region of the base substrate, with the
exception of a pad portion of the flexible region; placing prepregs
on upper and lower surfaces of the base substrate corresponding to
a rigid region, placing base copper plates corresponding to the
rigid region and the flexible region on the prepregs, and then
collectively laminating the placed prepregs and base copper plates
to form a rigid region and a flexible region; forming external
circuit patterns electrically connected to each other on the rigid
region, while protecting the base copper plate corresponding to the
flexible region; and removing the base copper plate corresponding
to the flexible region.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A to 1I are sectional views sequentially showing a
conventional process of fabricating a flying tail type
rigid-flexible PCB;
FIGS. 2A to 2I are sectional views sequentially showing a process
of fabricating a rigid-flexible PCB, according to the present
invention; and
FIG. 3 is a sectional view showing the structure of the
rigid-flexible PCB, fabricated using the method of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a detailed description will be given of a method of
fabricating a rigid-flexible PCB, according to the present
invention, with reference to the appended drawings.
FIGS. 2A to 2I are sectional views sequentially showing a process
of fabricating a rigid-flexible PCB, according to the present
invention.
As shown in FIG. 2A, a polyimide copper clad laminate 110
comprising a polyimide layer 111 and a copper foil 112 is
provided.
Polyimide is a polymer material suitable for working under
conditions of high temperature and high pressure, thanks to its
excellent wear resistance, heat resistance, self-lubricating
ability, creep resistance, electrical insulating properties, and
plasma properties in a vacuum.
As shown in FIG. 2B, an etching resist pattern 120 for the
formation of an internal circuit pattern is formed on the copper
foil 112.
To form the etching resist pattern 120, a circuit pattern printed
on an artwork film should be transferred onto the substrate.
Although the transferring process may be variously conducted, it
may be mainly carried out using a photosensitive dry film in such a
manner that the circuit pattern printed on the artwork film is
transferred onto the dry film using ultra violet (UV) light.
Thus, the dry film having the transferred circuit pattern may act
as an etching resist. In the case where an etching process is
performed using the dry film as an etching resist, the copper foil
112 in the region on which the etching resist pattern 120 is not
formed, is removed, thus forming an internal circuit pattern having
a predetermined shape, as shown in FIG. 2C.
After the internal circuit pattern having a predetermined shape is
formed, the etching resist pattern 120 remaining on the non-etched
copper foil 112 is removed, thereby completing a base substrate, as
shown in FIG. 2D.
Then, in order to protect the internal circuit pattern
corresponding to a flexible region, which is to be formed on the
base substrate, with the exception of a pad portion of the flexible
region required for use in an external pad and a mounting pad, from
external environments, a coverlay 130 is processed to suit the
flexible region.
The coverlay 130 may be formed by attaching a polyimide film to the
flexible region having the corresponding internal circuit pattern,
with the exception of the pad portion of the flexible region, using
an adhesive, and then temporarily bonding the polyimide film
through manual soldering, as shown in FIG. 2E.
In the flexible region, the pad portion for use in an external pad
and a mounting pad is exposed as not covered with the coverlay
130.
After the formation of the coverlay 130, prepregs 140 are placed on
upper and lower surfaces of the base substrate corresponding to a
rigid region, after which base copper plates 150 are placed on the
prepregs 140 to correspond to the rigid and flexible regions.
Each of the prepregs 140 has a window corresponding to the flexible
region such that the prepreg 140 is laminated only on the portion
where the rigid region is formed. As such, the prepreg 140 is
formed in a semi-cured state by infiltrating a thermosetting resin
into glass fibers, and thus functions to confer mechanical strength
to the rigid region and also may act as an adhesive between the
base substrate and the base copper plate 150 upon the subsequent
compression procedure.
The base copper plate 150 placed on the prepreg 140 does not have a
window, to serve as the external circuit pattern of the rigid
region and the protection plate of the pad portion of the flexible
region.
Thereafter, the base copper plate 150, the prepreg 140, the base
substrate, the prepreg 140, and the base copper plate 150, in that
order, are laminated and compressed under conditions of
predetermined temperature and pressure, thereby forming both the
rigid region, in which the internal circuit pattern 112 is
incorporated into the prepreg 140, and the flexible region having
the internal circuit pattern 112, part of which is coated with the
coverlay 130, the other part of which is exposed to form the pad
portion, as shown in FIG. 2F.
After the layers are compressed, a through hole 160 for electrical
connection between internal and external layers of the substrate is
formed, as shown in FIG. 2G.
The through hole 160 results from computer numerical control (CNC)
drilling at the predetermined position of the rigid region,
resulting in a plated through hole 160 penetrating through the
substrate.
Thereafter, the through hole 160 and the base copper plate 150 are
plated with copper, thus forming a copper plated layer 170, as
shown in FIG. 2H.
The copper plated layer 170 formed on the through hole 160 acts to
realize the electrical connection between the internal and external
layers, while the copper plated layer 170 formed on the base copper
plate 150, along with the base copper plate 150, constitutes a
plated layer 180, which is then formed into an external circuit
pattern.
After the copper plated layer 170 is formed, a photolithographic
process is conducted on the plated layer 180 using a dry film, to
form a desired external circuit pattern, as shown in FIG. 2I.
As such, the external circuit pattern is formed only on the rigid
region, so that the base copper plate 150 and the plated layer 180
corresponding to the flexible region function to protect the pad
portion exposed for use in an external pad and a mounting pad. That
is, when the external circuit pattern is formed, the flexible
region should be protected by the base copper plate 150 and the
plated layer 180 so that the exposed pad portion thereof is not
damaged by the etching process.
In addition, for easy removal of the base copper plate 150 and the
plated layer 180 corresponding to the flexible region, the base
copper plate 150 and the plated layer 180 corresponding to the
flexible region are formed to be about 0.05.about.5 mm larger than
the flexible region. In addition, the edge portion of the base
copper plate 150 and the plated layer 180 corresponding to the
boundary between the flexible region and the rigid region is
processed using a CNC drill or a steel rule die, whereby the
subsequent removal procedure of the base copper plate 150 and the
plated layer 180 becomes easier.
Then, the base copper plate 150 and the plated layer 180
corresponding to the flexible region remaining to protect the
exposed pad portion for use in an external pad and a mounting pad
are physically removed by manual labor or using an automated
machine. Further, with the goal of preventing a solder bridge
phenomenon between external circuit patterns during a soldering
process while protecting the external circuit pattern, the
resultant substrate is coated with PSR ink and then surface
treated. Thereby, as shown in FIG. 3, a flying tail type
rigid-flexible PCB, without the need for a resist cover, is finally
obtained.
As described above, the present invention provides a method of
fabricating a rigid-flexible PCB. According to the method of the
present invention, after an external circuit pattern is formed, the
base copper foil of a flexible region is window etched to protect
the exposed pad portion, instead of using a conventional resist
cover formed of heat-resistant tape or peelable ink. Thereby, the
inventive method is advantageous because the fabrication processes
are simplified and price competitive power is increased.
In addition, since heat-resistant tape and peelable ink are not
used in the present invention, conventional problems, that is,
contamination and damage of the circuit pattern due to the presence
of residue thereof, may be prevented, thus greatly increasing
reliability.
The embodiment of the present invention has been disclosed for
illustrative purposes, those skilled in the art will appreciate
that various modifications, additions and substitutions are
possible, without departing from the scope and spirit of the
invention as disclosed in the accompanying claims.
* * * * *